The present invention relates to chisels, and relates particularly, but not exclusively, to chisels for cutting a channel.
Often there is a need to form a channel in a work piece into which cables or pipes can be laid. The usual work piece is a concrete or similar hard ceramic surface. The ideal choice of tool is a chisel specifically shaped to cut such a channel, hereinafter referred to as a “channel chisel”. In use the channel chisel can be connected to a reciprocating hammer apparatus like, for example, a portable power tool called a hammer, which repeatedly hits the channel chisel to transmit impact forces to it.
EP0519493 discloses a channel chisel comprising a shaft for insertion into the hammer and a tip that is inclined in relation to the axis of the shaft. The tip is U-shaped in cross-section and includes a flute to facilitate the removal of debris cut from the channel. A wing is formed on each side of the shaft. The wings are folded midway along their length so that a portion of each wing is inclined in relation to the longitudinal axis of the shaft. This enables that part of the wings to be supported on the upper surface of the work piece to fix the angle of the channel chisel in relation to the work piece and the depth at which the tip cuts into the work piece.
The channel chisel of EP0519493 suffers from the drawback that while the channel chisel is reciprocated up and down by the hammering forces of a hammer apparatus, the wings formed on either side of the shaft must repeatedly impact the upper surfaces of the work piece in which the channel is formed. This results in damage to the upper surface of the work piece at the edges of the channel. In order to minimise the damage caused, the wings have generally flat lower surfaces to reduce the pressure applied to the work piece by the impact forces. However, if the user wishes to increase the depth of the channel cut, the channel chisel must be tilted forward so that the front ends of the wings, instead of the flat lower surfaces, are supported by the upper surfaces of the work piece. This reduces the surface area of the wings contacting the work piece which results in an increase in the pressure applied at the points of contact and the consequential damage caused to the work piece. The user has no option but to tilt the channel chisel forward to increase the depth of channel cut as the wings are rigidly fixed to the channel chisel and their orientation cannot be altered.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.